This invention relates to endless belt filters, and more particularly to such filters for separating liquids and solids from a mixture.
Endless belt filters commonly comprise an endless belt of permeable material onto the upper run of which is fed the mixture to be separated. At least one suction tray is located beneath the upper run of the belt to move along with the belt and to receive therein liquid from the mixture that passes through the belt, a vacuum applied to the suction tray serving to draw the liquid from the suction tray for subsequent disposal thereof.
Heretofore it has been common practice to interconnect the vacuum source with the suction trays by means of flexible hoses to accommodate the relative movement between the source and the trays. However, the use of such hoses invariably imposes undesirable restrictions upon, for example, the temperature of the products, the volume of the products and the range of the products that can be safely handled by the filter arrangement, as well as imposing undesirable physical forces on the trays themselves.
It has been proposed, for example in EP-A-0511710, to utilise a telescopic connection between the vacuum source and the suction trays, which overcomes some of the aforementioned restrictions. However, such an arrangement introduces further problems in that, under vacuum conditions, there is a tendency for the telescopic connection to close itself thereby imposing further substantial and undesirable sideways forces on the suction tray.
Additionally, such a system must of necessity incorporate extremely well-fitting seals to maintain a sealed system. The relatively high temperate under which the filters can operate, together with the aggressive nature of the mixtures being handled, which often causes crystallisation, will inevitably serve to cause ongoing deterioration in the seals.
It has also been proposed, for example in EP-A-0688592, to provide, along one or both sides of the belt, a stationary suction box incorporating a slot in which the or each movable suction tray slides. Again, such an arrangement will require extremely accurate engineering to ensure continuous sealing between the or each stationary suction box and the movable suction trays, particularly bearing in mind that the former are typically up to 20 meters long.